Modern medical practice requires the use of aseptic materials and devices, many of them meant for repeat use. In order to achieve this sterilization, processes are needed, at the manufacturer, and also at the hospitals for treatment of reusable materials and devices.
Typical of materials which are reused in the hospital environment and require repeated sterilization are major surgical instrument trays, minor surgical kits, respiratory sets, fiber optics, scopes and breast pumps.
There are a wide variety of medical devices and materials that are to be supplied from the manufacturer already packaged and sterile. Many of these devices and materials are disposable. Typical of this group are barrier packs, head coverups and gowns, gloves, sutures and catheters.
One major sterilization process in present use is that which employs ethylene oxide (EtO) gas at up to three atmospheres of pressure in a special shatter-proof sterilization chamber. This process, in order to achieve effective asepsis levels, requires exposure of the materials to the gas for at least one hour followed by a minimum of twelve hours, or longer, aeration period. The initial gas exposure time is relatively long because the sterilization is effected by alkylation of amino groups in the proteinaceous structure of any microorganism. EtO sterilization requires the attachment of the entire EtO molecule, a polyatomic structure containing seven atoms to the protein. This is accompanied by the requirement of hydrogen atom rearrangement on the protein to enable the attachment of EtO. Because of the space factors governing the attachment of such a bulky molecule, the process needs to be carried out at high pressure and be extended over a long period of time. It is, therefore, deemed very inefficient by the industry at large.
Perhaps the chief drawback to this system, however, is its dangerous toxicity. Ethylene-oxide (EtO) is a highly toxic material dangerous to humans. It was recently declared a carcinogen as well as a mutagen. It requires a very thorough aeration process following the exposure of the medical materials to the gas in order to flush away EtO residues and other toxic liquid by-products like ethylene glycol and ethylene chlorohydrin. Unfortunately, it is a characteristic of the gas and the process that EtO and its toxic by-products tend to remain on the surface of the materials being treated. Accordingly, longer and longer flush times (aerations) are required in order to lower the levels of these residues absorbed on the surface of the materials to a safe operational value. A typical volume for each batch using this EtO process is 2 to 50 cu. ft. within the health care environment.
A number of other approaches for performing sterilization have also been employed. One such process is steam autoclaving. However, this requires high temperature and is not suitable for materials which are affected by either moisture or high temperature. Another approach utilizes either x-rays or radioactive sources. The x-ray approach is difficult and expensive. The use of radioactive sources requires expensive waste disposal procedures, as well as requiring radiation safety precautions. The radiation approach also presents problems because of radiation-induced molecular changes of some materials, which, for example, may render flexible materials brittle.
It is therefore a primary object of the present invention to provide a process and apparatus for dry sterilization of medical devices and materials, which can be operated efficiently, both with respect to time and volume.
It is another object of the present invention to provide a safe, nontoxic, process for the sterilization of medical devices and materials, a process which does not employ toxic feed gases and one which does not yield toxic adsorbed surface residues.